Wednesday, June 17, 2009

Comparison of the sexuality of Humans, Common Chimpanzees and Bonobos

When first considering this title, it may seem a bit perverse to be delving into the details of human, chimpanzee and Bonobo sexuality. However, when considering Darwin and the theory of evolution, it is integral to discover the mating habits and social norms of all species, especially ones that are so closely related to our own, in order to further our understanding of human evolution. Homo sapiens, the Common Chimpanzee and Bonobos, otherwise known as pygmy chimpanzees, all share a common ancestor. Between these species, there are many noted areas of similarity and disparity within behaviour and physical appearance. One area that has been of particular interest to many researchers is that of social sexual behaviour. Well known Homo sapiens are usually set apart from other mammals due to our ability to conduct ‘higher thought’ processes. Nevertheless, social sexual behaviour is also a major characteristic that separates humans from most other species. Sexual behaviour of humans is fairly distinct because they are not sexually active solely for reproductive purposes. In the human community, sexual intercourse also plays an important role socially, by creating strong bonds between individuals by increasing physical intimacy, it is the foundations of many social hierarchies and there is also a hedonistic factor as enjoyment of the activity is a large driving force behind copulation. Evidence to support this in humans, is the creation of contraceptive techniques. Humans not only have sexual intercourse when procreation is not intended, but they go one step further and take measures to ensure that reproduction is actually prevented. This is a behaviour that is almost certainly unique to the human species, even if sex as a social role is not. Bonobos are another species that uses sexual intercourse in a social context, with the same benefits as humans, such as stronger bonding and social hierarchies. It also has been seen to maintain a more peaceful environment amongst their community as aggression amongst the males can be vented through sexual acts. Atypically for species in the mammal genre, the female Bonobos are hierarchically more dominant.5 It has been theorised that this is due to the bonds that are formed between females. Wrangham, a leading primatologist, hypothesises that this grouping of females is a counter strategy to the male reproductive strategies as groups of females are greater at attracting groups of males.1 On the other hand, the Common Chimpanzee do not hold the same principles of social sexual behaviour and society tends have a more aggressive atomosphere. The Common chimpanzees have a patriarchal society where the males are dominant and, as with most animals, sexual intercourse is purely for reproduction and advancement of the species. The Bonobos and the common chimpanzees, are part of the same genus and have many similarities mainly physically and biologically, an example being the female swelling cycle. Impending ovulation the sexual skin surrounding the perineum of the female primate, swells and reddens, and is usually shows a conspicuous maximum tumescence around the presumed time of ovulation.4 Studies have shown that in both species this swelling has a direct affect on the sexual arousal of the males. This has the obvious evolutionary advantage of attracting males sexually, when the female is most fertile. The results of the studies, show that the Bonobos seem to have a longer span of maximum tumescence compared to the common chimpanzees, although this could be a discrepancy of only 1-3 days. With this in mind, another point of comparison that could be addressed is that of the cycles of arousal between the species. In humans, sexual arousal for females is not limited by the time of ovulation as it is with most other mammals, there are only periods of heightened sensitivity. This supports the idea of a more socially orientated sexual behaviour as sexual intercourse can be initiated at any point. Bonobos are similar to humans in this instance, although they have a more obvious display of when they are at maximum tumescence. Unlike the common chimpanzees, instead of a few days out of her cycle, the female bonobo is almost continuously sexually active and attractive. The position of sexual intercourse is one of the more shocking similarities between Bonobos and Humans. In contrast to most other primates, the Bonobos mate in what was long considered to be a uniquely human fashion. Their sexual activities vary in position and sexual contacts, including face to face copulation. The common chimpanzees have a more typical mating ritual which is generally associated with mammals, with the male approaching from behind the female. Female bonobos also partake in a sexual activity known as genito-genital rubbing, where the two females rub together their gential swelling laterally together. It is thought that this female-female interaction helps reinforce the strong bonds between the females and contributes to the female dominance.2 Females amongst the common chimpanzees are not so well attached and so such activities do not take place in this species’ communities. Male bonobos have also been seen to participate in homosexual activities. Examples are where one male briefly rubs his scrotum against the buttocks of another. Another example is the phenonmenon of ‘penis fencing’ whereby two males hang face to face from a tree while rubbing their erect penises together.2 It is unsure what benefits such acts of homosexuality can have, seeing as there is no reproductive advantage, however one explanation available is that it is a way of resolving disputes amongst individuals of the group as an act of peacemaking. There has also been some evidence of masturbation by both female and male bonobos, an action that is almost unheard of outside of a human context. This fact serves to further prove the idea that the bonobos enjoy a highly sexually based society. Finally the most significant difference between humans and the two species of chimpanzee is the tendancy to only have one sexual partner at a time. This is not a behaviour that it found amongst the primates as each female and male have multiple partners.6 In the wild this has its advantages as it lowers the occurance of infanticide by males as there is no way of being sure which male the offspring belongs to. Also, unlike most species in the animal kingdom, the time when a person reaches physical maturity is not directly correlated to when a person first takes part in sexual intercourse. In conclusion, Humans, The common Chimpanzee and Bonobos, despite being derived from a common ancestry have very some very different social behaviours concerning sexuality. Out of the three species Bonobos and Humans arguably have the more similar behaviours as their community as a whole largely revolves around a sexual concept. Sexuality moulds the way Bonobos interact with eachother as it does within human society. Even the way the act is carried out greatly resembles that of humans. The only major difference is that humans usually maintain a single partner throughout life, and tends to only reproduce with that partner, whereas the primates have multiple partners. Also as soon as the primate reaches physical maturity, they are then expose to sexual activities, whereas this is not necessarily the case in homo sapiens.

Interesting, informative but a major conclusion isn't supported by the article. A single partner for life isn't the norm in human society and even where it appears to be so, "cheating" is not uncommon. Serial monogamy is also common (divorce rate 50% in the USA? not to mention that many people will have multiple sexual partners before eventually "settling down" to establish a family with just one), and in some societies a wealthy man may have multiple wives, e.g. the Arab harem.